.\" RCSid "$Id: ra_ppm.1,v 1.3 2004/03/26 22:58:20 greg Exp $"
.TH RA_PPM 1 2/10/99 RADIANCE
.SH NAME
ra_ppm - convert RADIANCE picture to/from a Poskanzer Portable Pixmap
.SH SYNOPSIS
.B ra_ppm
[
.B \-r
][
.B \-a
][
.B \-b
][
.B "\-s maxv"
][
.B "\-g gamma"
][
.B "\-e +/-stops"
]
[
.B input
[
.B output
]
]
.SH DESCRIPTION
.I Ra_ppm
converts between RADIANCE and Poskanzer Portable Pixmap formats.
The
.I \-g
option specifies the exponent used in gamma correction;
the default value is 2.2.
An exponent of 1 turns gamma correction off.
The
.I \-e
option specifies an exposure compensation in f-stops (powers of two).
Only integer stops are allowed, for efficiency.
The
.I \-r
option invokes a reverse conversion, from a Pixmap to
a RADIANCE picture.
If the output file is missing, the standard output is used.
If the input file is missing as well, the standard input is used.
.PP
The
.I \-a
option produces a standard ASCII Pixmap representation instead of
the default binary file.
The file is much larger and the conversion is much slower, which is
why this format is not normally used.
The
.I \-b
option forces greyscale output.
The
.I \-s
option controls the output scale, which is 255 by default.
If this value is set above 255, then two bytes will be output for each
component in binary mode.
This may not be understood by some PPM readers, which do not understand
files with maximum values greater than 255.
The maximum allowed setting for this parameter is 65535.
.PP
With the
.I \-r
option, the type of the Pixmap input file is determined automatically.
.I Ra_ppm
will read either greyscale or color Pixmaps, with any precision up
to a maximum scale of 65535.
.SH NOTES
The Poskanzer Portable Bitmap Plus package contains translators between the
Pixmap format and many of the dozen or so image
file "standards" that exist.
At the time of this writing, the software is free and available by
anonymous ftp from export.lcs.mit.edu (18.30.0.238) in the file
"contrib/pbmplus.tar.Z".
.SH AUTHOR
Greg Ward
.SH ACKNOWLEDGEMENT
Work on this program was initiated and sponsored by the LESO
group at EPFL in Switzerland and Silicon Graphics, Inc.
.SH "SEE ALSO"
pfilt(1), ra_bmp(1), ra_bn(1), ra_pr(1), ra_pr24(1), ra_t8(1), ra_t16(1),
ra_tiff(1), ximage(1)
